Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to a valve used to automatically switchover from one pressure source to a backup or reserve pressure source upon the depletion or failure of the primary source such as with a system utilizing compressed gas cylinders.
2. Description of Prior Art
This invention relates generally to a valve system for the automatic switchover from one source of pressurized fluid to a second, or reserve, source in response to the depletion or failure of the primary pressure source. The invention specifically relates to a valve used to switchover from one compressed gas cylinder to a backup or alternate cylinder.
Prior art addressed automatic switchover utilizing the xe2x80x9cshuttle valvexe2x80x9d principle involving actuation by electrical solenoids and diaphragm regulators, U.S. Pat. No. 2,768,640 to Zimmer (1953). Others relied on a plurality of check valves, pistons, springs, and cavities for direction and/or control as in U.S. Pat. No. 3,131,708 to Knight (1964). Assemblies consisting of spools, diaphragms, springs, valves, and detents as in U.S. Pat. No. 4,674,526 to Athanassiu (1987) improved the operation of the valve but remained complex and expensive to build.
Simplification of the switchover valve was achieved through the utilization of a spool as evidenced in U.S. Pat. No. 3,533,431 to Kuenzel and Gilmore (1970). Spool valves by the nature of their design can be subject to false switchover, reverse flow, and a less than optimum operating pressure range. These important functional issues were overcome through the use of expensive check valves and/or pressure regulators incorporated in a switchover valve system as in the U.S. Pat. No. 4,889,152 to Wilson (1989). U.S. Pat. No. 5,014,733 to Wilson (1991) combined various features into one device that is expensive to manufacture and is susceptible to issues involving source pressure. U.S. Pat. No. 6,296,008 to Boyer and Pryor (2001) utilizes a locking mechanisnm which again, adds costs, but is effective in preventing false switchovers and also eliminates the need for check valves but still requires the use of expensive pressure regulators to insure reliable operation.
To insure reliability, costly features are incorporated into switchover valve systems. The disadvantages of the know switchover valve systems are:
(a) Susceptibility to reverse flow, requiring the added cost of check valves.
(b) Limited functional pressure range requiring the added cost and complexity of pressure regulators.
(c) Susceptibility to false or premature switching requiring mechanical locks to insure swift, accurate switching.
(d) Reliance on additional valving to isolate the switchover system during pressure source replenishment especially where compressed gas cylinders are being replaced.
There are several objects and advantages of the present invention including the provision of a switchover valve for the automatic switchover from a primary source of pressurized fluid (e.g. a compressed gas cylinder) to a second source in response to the depletion or failure of the primary pressure source that is:
(a) simpler, more compact, and is less costly to manufacture;
(b) more reliable given it""s simple construction;
(c) a failsafe control which is immune to false switchover;
(d) impervious to reverse flow;
(e) more economical given that it affords the utilization of source pressure to it""s minimum but adequate, supply pressure prior to switchover;
(f) functional without the need for costly valving to isolate source pressure.
The present invention advances the prior art through simplification of operation and economy of construction. These and all other objects and advantages comprise a switchover valve system for delivering a pressurized fluid from a plurality of sources such that automatic switchover occurs in response to the depletion or failure of a pressure source, which switchover to another pressure source is not effected by source pressure differentials, which switchover occurs at a predetermined source pressure, which operation of the valve is unencumbered during switchover and therefore failsafe, free of reverse flow, and reliable in operation.
The above is generally embodied in this invention for the automatic switchover from one source of pressurized fluid to another source of pressurized fluid in response to the failure or depletion of the one source wherein a tubular valve body comprises two inlets, one for each said source, for communication with an outlet. A spool, with a tubular feature, is moveable in the tubular body, which sets one inlet in communication with the outlet such that the other inlet is closed to the outlet. The spool""s tubular feature directs the communicated (inlet) pressure upon its self such that it holds the spool position against the apposing axial spring which is biased against said pressure. The closed inlet is rendered ineffectual in this position. The spool is responsive to the spring bias pressure such that with the depletion of said holding pressure the spring bias overcomes said holding pressure at a predetermined value and said spring moves the spool unencumbered to a position such that the previously blocked inlet is opened releasing fluid pressure which sets the spool in communication with the outlet such that the original inlet is closed to the outlet. The spool""s tubular feature directs the newly communicated (inlet) pressure upon it""s self such that it holds the spool position against the axial spring, which is biased against said pressure; the closed original inlet is rendered ineffectual in this position.